Field of the Invention
The invention relates to a radar method, in particular for road vehicles, having at least one radar beam, in which digitized and recorded samples that are received during two modulation phases in each modulation cycle of mixed signals formed from transmitted and received signals are subjected separately to a fast Fourier transformation in successive measurement cycles per radar beam, each measurement cycle includes a modulation cycle formed from a rising and a falling modulation phase of the radar signal and a subsequent evaluation pause for the received echo signals, in a digital signal processor, in order to determine object frequencies which are assigned to the target objects, per measurement cycle from the maxima contained in the frequency spectra derived therefrom, object tracks are formed from the object frequencies which are stored over a number of measurement cycles for each target object and separated according to rising and falling modulation phases, the object tracks describing a previous time-domain behavior of the object frequencies, estimated values for the object frequencies to be expected in the next measurement cycle are formed from the previous behavior of the object tracks, and the object frequency pairs which have the respectively smallest error are assigned to one another after calculation of an error from the object frequencies and from estimated values obtained from the object tracks, and correct values for distance and relative speed of at least one target object are calculated from the pairs.
The invention also relates to a device for carrying out the method, including a digital signal processor which produces triangular-waveform digital modulation signals that are converted in a D/A converter of an interface module into analog signals and are processed in a radar front end to form modulated radar signals that are transmitted and received by at least one antenna, and a mixing and filtering device for the production of mixed signals from the transmitted and received signals which are converted in an A/D converter of the interface module into digital signals and are supplied to the signal processor for further processing.
Such a radar method, in particular for road vehicles, and a device (radar set) for carrying out that method are described in Published International Patent Application PCT/EP94/03646 (referred to below as the "previous method"), which has a later publication date than the effective filing date of the instant application, but forms the basis of the present invention. That device is a cost-effective FMCW radar set having a digital signal processor which controls at least one antenna through an oscillator and produces a mixed signal from transmitted and received signals which are modulated with a triangular waveform. The mixed signal is subjected to fast Fourier transform in each modulation phase (up or down) of each measurement cycle in order to obtain object frequencies from the determined maxima which are assigned to each target object, from which object tracks are formed that extend back over a plurality of measurement cycles and are used to form estimated values for the measurements which can be expected in the next measurement cycle at the object frequencies. The mutually associated object frequencies fu=.vertline.fr-fv.vertline. and fd=.vertline.fr+fv.vertline. of both modulation phases of a measurement cycle are determined, and the distance e.about..vertline.fu+fd.vertline. and relative speed vr.about..vertline.fu-fd.vertline. of each target object are determined from them in a known manner.
FMCW radar methods are generally known, for example from:
The publication by E. Baur, entitled: Einfuhrung in die Radartechnik/Studienskripten [Introduction to Radar Technology/Study Scripts], Teubner, 1st Edition, Stuttgart 1985, pages 124 to 133;
German Published, Non-Prosecuted Application DE 25 14 858 A1;
German Published, Non-Prosecuted Application DE 29 00 825 A1; and
German Published, Non-Prosecuted Application DE 40 40 572 A1.